The present invention is amongst others applicable to the enveloping and/or supporting substrate of an electronic device comprising a conductive polymer with e.g. an electronic device, a photovoltaic cell and/or semi-conductor devices.
Optical glass has been previously used in electronic display applications as substrate because it is able to meet the optical and flatness requirements and has thermal and chemical resistance and good barrier properties. Main disadvantage of the use of glass is related to its weight, inflexibility and fragility. For this reason flexible plastic materials have been proposed as replacement for glass.
Disadvantages of the use of polymeric substrates are their lower chemical resistance and inferior barrier properties.
It is a known fact, that atmospheric pressure glow discharge plasmas used for deposition of a chemical compound or chemical element suffer from dust formation by which formation of a smooth surface cannot be obtained and the used equipment will accumulate the dust in a short period of time resulting in products with worse barrier properties as the roughness of the barrier layer.
In the article “Deposition of dual-layer of SiOx/SiOxCyNwHz by Townsend dielectric barrier discharge” by Maechler et al. it is described that a dual layer barrier is formed on a polymer substrate. The method uses an atmospheric pressure Townsend discharge mode (different from Glow discharge mode) in a treatment space. A first (shield) layer is deposited of organic material SiOxCyNwHz after which a SiOx barrier layer is deposited. The article also discloses that a SiOx coating directly deposited on a polymer in the atmospheric pressure Townsend discharge plasma induces damages of the polymer resulting in poorer barrier properties than for uncoated polymer. The best result reported to be achieved is a 10-fold improvement of the barrier properties (Barrier Improvement Factor BIF=10).
In the international patent application WO2007139379, filed by applicant, the process is described for depositing inorganic layers on substrates using a predefined ton time and a predefined gas-composition for preventing the formation of dust in the treatment space.
Further WO2006097733 describes a method of making a composite film with a barrier by applying a planarising coating composition first and then providing a barrier film by high-energy vapour deposition.
WO2010092383 and WO2010092384, both filed by applicant, describe processes of a two layer deposition on a polymer substrate using an atmospheric pressure glow discharge plasma in a treatment space formed between two or more opposing electrodes connected to a power supply using a conditioned gas composition in the treatment space comprising a precursor and oxygen. In both processes the second layer of inorganic material is deposited on the first layer in a treatment space wherein the oxygen has a concentration of 3% or higher, and the power supply is controlled to provide an energy across a gap between the two or more opposing electrodes of 40 J/cm2 or higher.
In many manufacturing processes involving glass substrates, such as the process of manufacturing OLED devices, there is a desire to replace glass substrates with low weight, flexible polymeric substrates using polymers with a very thin amorphous layer of metal oxide with improved barrier properties.
It is an object of the invention to provide a method for creating an improved barrier on a substrate, in particular a flexible substrate.